1. Field of the Invention
The present invention relates to warp beaming for a warp knitting machine or a loom, especially to a method for forming a warp beam of uniform diameter, even in a selvage portion while controlling winding tension of a warp.
2. Description of the Related Art
In a conventional warp knitting machine, a predetermined number of warp beams are fixedly held on one common shaft to form an integrated single warp beam. A sheet consisting of a plurality of parallel warps is withdrawn therefrom by rotation of the shaft for a knitting operation. If the warp beams are different in diameter (i.e., "inter-beam diameter difference") or if a single beam has differences in diameter (i.e., "intra-beam diameter difference"), the tension of the warp in the sheet tends to vary along the width of the sheet. The difference of the tension causes a wale streak in the resultant fabric. A similar drawback occurs in a loom for producing a woven fabric. Therefore, it has been desired for a long time to provide a method and apparatus for obtaining warp beams of a uniform diameter even in a selvage portion.
Especially, since a barrel 31 on which the beam is formed has tapered flanges 32 at opposite ends thereof, as shown in FIG. 3, the local diameter of the beam (i.e., a diameter of the beam at a certain widthwise position) at the selvage portions tends to be irregular relative to the middle portion of the beam, because the distance between the flanges 32 increases the further out from the barrel. In the prior art, to avoid this intra-beam diameter difference, local diameters of various portions of the beam on the warper are frequently inspected during the winding operation by stopping the machine. If there is a certain difference between measured diameters, a width and/or a position of a reed is adjusted to compensate for the distribution of the warp on the beam. It is apparent that this method is very cumbersome and lowers productivity.
In Japanese Examined Patent Publication (Kokoku) No. 56-34661, to avoid an inter-beam diameter difference, a correlation coefficient is calculated from an accumulated warp length already wound on a beam and accumulated revolutions of the beam corresponding thereto and is compared to a predetermined reference correlation coefficient, whereby the total winding tension is controlled to compensate for the beam diameter. Also in Japanese Examined Patent Publication (Kokoku) No. 56-34662, a correlation coefficient is calculated from a rotational rate of a warp beam and a winding speed of warp and is compared to a predetermined reference correlation coefficient, whereby the total winding tension is controlled to compensate for the beam diameter. These methods, however, are effective only for inter-beam diameter differences and cannot improve the intra-beam diameter difference.